There are two corporation tax returns in your first year because a Corporation Tax accounting period cannot be longer than 12 months. This means you will have two deadlines.
For example, if you incorporate your company on 12th September 2023 and start trading straight away, you will have two corporation tax returns, one for the period 12th September 2023 to 11 September 2024, and another for the 12th September 2024 to 30th September 2024 (your financial year end).
In the subsequent financial years, you will only have one tax return to file each year, unless you change the accounting period date.
Your Company Accounts that are filed to Companies House would cover the extended period 12th September 2023 to 30th September 2024 – only one set of accounts would be filed.